Magnetron



Feb. 12, 1957 L. P. SMITH MAGNETRON Filed April 24, 1948 3 Sheets-Sheet1 INVENTOR LLOYD P. SMITH Feb. 12,, 1957 P. SM'ITH 2,731,476

MAGNETRON Filed April 24, 1948 s Sheets-Sheet 2 E Gil/F7 PER Feb, H2,1957 L. P. SMITH 2,781,476

MAGNETRON Filed April 24, 1948 3 Sheets-Sheet 3 United States PatentOfifice 2,781,476 Patented Feb. 12, 1957 2,781,476 MAGNETRON Lloyd P.Smith, Ithaca, N. Y., assigrror to Radio Corporation of America, acorporation of Delaware Application April 24, 1948, Serial No. 23,045 41Claims. (Cl. 315-3957) My invention relates to generators of highfrequency radio waves using cavity resonators and more particularly toelectron discharge devices such as magnetrons utilizing cavityresonators and to means for varying the generated frequency of suchelectron discharge devices.

This application is a continuation-in-part of my copending application,Serial No. 563,732, filed November 16, 1944, now abondoned. Saidcopending application was re-filed prior to abandonment as acontinuation application Serial No. 285,627, filed May 2, 1952, now U.S. Patent No. 2,695,373, granted November 23, 1954.

it has become necessary to be able to vary the generated frequency overa limited frequency range of a magnetron or other ultra high frequencygenerator using cavity resonators as tank circuits. It is desirable tohave the frequency change occur as a prescribed function of the time andwith greater rapidity than is practical by mechanical tuning of theresonator. It is further desirable that the power output should beconstant over the variable frequency range.

It is, therefore, an object of my invention to provide a high frequencygenerator utilizing a cavity resonator with means for varying ormodulating the generated frequency.

Another object of my invention is to provide an electron dischargedevice utilizing cavity resonators and which can. be frequencymodulated.

More specifically it is an object of my invention to provide a magnetronutilizing cavity resonators and which can be frequency modulated byelectronic means.

The novel features which I believe to be characteristic of by inventionare set forth with particularity in the appended claims, but theinvention itself will best be understood by reference to the followingdescription taken in connection with the accompanying drawing in whichFig. 1 is a perspective view with parts broken away of one embodiment ofmy invention; Figs. 2, 3, and 4 are diagrams which help to explain theprinciples of my invention; Figs. 5 and 6 are equivalent circuitsshowing operation of apparatus made according to my invention; Fig. 7 isa graph illustrating the operation of a device made according to myinvention; Fig. 8 is a plan view of a magnetron incorporating myinvention with part of the shell cut away; Fig. 9 is a section on anenlarged scale taken along the line IXIX of Fig. 11; Fig. 10 is asection taken along the line X-X of Fig. 8; Fig. 11 is a side view ofthe magnetron shown in Fig. 8 with part of the shell removed; and Fig.12 is a section taken along the line XIIXII of Fig. 11.

The method and apparatus employing my invention can best be understoodby reference to Fig. l which utilizes a cavity resonator, the resonantfrequency of which can be changed by electronic means. In the deviceshown I provide an evacuated envelope 10 containing a rectanguiar cavityresonator 11 having dimensions X, Y, and Z. The cavity resonator isprovided with oppositely disposed apertures 12 and 13 in opposite wallsthereof through which an electron beam is directed. The electron beam isprovided by means of an indirectly heated cathode 14 and can becontrolled by a grid 15. An electrode 16 on the opposite side of theresonator and in the path of the electron beam may be used in place ofor in combination with the grid 15. Transfer of energy to and from thecavity resonator 11 may be had by means of a coaxial line 17 coupled tothe resonator by a loop 17 terminating within the resonator. A constantmagnetic field H is produced along the path of the beam of electrons bysuitable means, such as a magnet having pole pieces 18 and 19. Themagnet may be either a permanent magnet or an electroma-gnet. A controlinput circuit includes 'a transformer 20, and the voltage sourcesinclude grid biasing voltage source 21, cathode heater voltage source22, voltage source 23 for applying a positive potential to the resonator11 and voltage source 24 which may apply either a positive or negativevoltage to the electrode 10, depending upon whether the electrode is tobe used as a collector or reflector. Alternative arrangements forcontrolling the beam include a circuit having a transformer 25 forapplying varying accelerating voltages to rwonator 1i and a circuitincluding a transformer 25' connected to the electrode 16 for varyingthe voltage applied to this electrode when used as a control electrodeto reflect electrons back into the resonator.

in order to set up an alternating electric field within the resonatorsome form of driving means is necessary. In the arrangement shown acavity resonator magnetron 26 whose frequency is to be controlled isused as the driver. The magnetron is provided with a cathode 27 andradially directed vane elements 28, the inner edges of which provideanode segments. The wall of the envelope of the magnetron, which is ametallic envelope, and the vanes or slats 28 form cavity resonatorsbetween adjacent anode segments. This form of magnetron is well known. Amagnetic field parallel to the cathode and between the cathode and theanode is provided by suitable means, not shown. The coaxial line 17 hasa coupling loop 29 coupled to one of the magnetron resonators betweenadjacent anode segments. The coupling loop'17 of coaxial line 17 isoriented in the resonator 11 in a plane perpendicular to the beam paththerein, so that high frequency electric and magnetic fields aregenerated in the resonator, with the electric field E in the directionindicated, inducing the desired mode of operation.

The constant magnetic field along the Z direction of the resonatorserves two purposes. It keeps the electron beam together and it is bymeans of this magnetic field that electrons are made to move in such away as to produce a large reactive effect in the interior of the cavityresonator. The cavity resonator is assumed to be excited at an angularfrequency to, with no electron beam present, for example by themagnetron 26 although it could be excited by other means. This frequencycorresponds to the normal mode of oscillation for which the electricfield is always parallel to the X direction of the resonator, that is,tranverse to the direction of flue electron beam.

When an electron has a linear velocity v in a direction at right anglesto a. uniform magnetic field H, it will describe a circular path. Thetime To required to traverse a complete circle is where m is the mass ofthe electron, le] is the absolute value of its charge and H is themagnetic field intensity. Hence, this period of rotation is independentof both the electrons linear velocity and the radius of its circularpath. The angular frequency of rotation is then When an electron beam ismade to traverse an oscillating cavity resonator, the resonant angularfrequency w of the particular mode of oscillation under considerationchanges from w to wfi-Aw. Where Am represents the shift in angularfrequency caused by the passage of the beam through the resonator. Themagnitude of the frewherelIol is the total beam current, a is thetransit angle of the electrons, e is the dielectric constant within theresonator, XYZ is the volume of the resonator, m is the resonant angularfrequency of the system before the electron beam is introduced,

and f(w) is the same function of J iil l w, u(1+k)ct, w-(1lc)a',7r3.1416, lc-;6- 0

(see Equation 92, page 655 of said paper). When the transit angle a isnot too small, the maximum frequency shift Aw occurs when w=(1-k) a-4radians. When the magnetic field is adjusted for maximum frequency shiftthe Aw 'is proportional to the square of the transit angle a. For valuesof magnetic field considerably different from that necessary to producemaximum shift, A can be shown to be approximately proportional to a.

In Fig. 7there is shown the relationship of the change in frequency tothe k ratio,

which is equal to l l l Fig. 7 gives an idea of the behavior and orderof mag nitude of the change in frequency Aw per milliampere of beamcurrent shown as a function of k for a 4000 megacycle rectangularresonator Y=Z=5.3 cm. and X=.2 0111., when the electrons in the beamhave been accelerated through 100 volts. From the curve it will be seenthat the frequency shift Aw can be positive or negative depending uponwhether it is less than or greater than one. Physically, as describedabove, this is due to the fact that when k is less than one the rotatingelectrons tend to fall behind the electric field, thus producing theeffect of a lagging current, that is inductance. On the other hand, whenk is greater than one, electrons get ahead of the field causing acapacitance effect and the frequency decreases.

The effectiveness of a given beam current in changing the frequency,that is in producing reactance, is the greatest When the magnetic fieldis adjusted to optimum con ditions for the transit time used. Using therelationship (1k) (1x4, given above, the two values of the ratio k formaximum frequency shift Aw for the rectangular cavity resonator XYZdescribed, having a dimension Z=5.3 cm., a resonant frequency of 4000megacycles and a. 100 volt beam, are approximately .98 and 1.02, forpositive and negative frequency shifts, respectively. Thus, Fig. 7 showsthat for the rectangular resonator described (n a value of magneticfield such that the ratio k is substantially different from .98 and 1.02.causes the efiect in the change of frequency to be hardly noticeable.

Thus, a means is provided for markedly changing the resonant frequencyof a cavity resonator by electrons when the magnetic field is suitablyadjusted. The frequency can be varied as an arbitrary function of thetime by varying the beam current or the electron transit angle, or both,appropriately with the time.

As pointed out above, changing either the electron current density orthe electron transit angle will produce a corresponding'change in theresonant frequency of the resonator 11. If a fixed voltage is applied tothe resonator 11 and an alternating voltage applied to the grid 15 bymeans of the input 2.0,the current density is varied and hence theresonant frequency of resonator 11 is varied. If the voltage applied tothe grid 15 is fixed and the accelerating voltage applied to theresonator varied by means of the input 25, the beam velocity and thetransit time and transit angle of the electrons through the resonatorare varied, thus again varying the resonant frequency of the resonator11. It may also be desirable to utilize the electrode 16 merely as areflector, sending the electrons back to the resonator to be collectedin the resonator. In this case the alternating variable voltage may beapplied'to the reflector 16 by means of the input circuit 25. It is, ofcourse, understood in all these cases that magnetron 26 acts as thedriver for the resonator to induce the alternating electric field in theproper mode for bringing about the action desired, the change infrequency in the resonator 11 being reflected into the resonators of themagnetron 26 to vary its frequency. Thus, an electronic means isprovided for frequency modulating a magnetron utilizing cavityresonators.

Thus, the tube shown in Fig. l, composed of an appropriate resonator andbeam supplying means and means for controlling the beam current or thetransit time, constitutes a reactance tube which when closely coupled toa high frequency system can be used to vary the resonant frequency ofthe system by introducing an almost pure inductive or capacitivereactance which can be varied with the time in any manner.

A better understanding of my invention may be had of the above byreferring to Figs. 2, 3, 4, 5, and 6.

Consider a pair of parallel plates P across which an alternatingpotential difierence is applied resulting in an electric field ofamplitude E and angular frequency w between the plates, as shown in Fig.4. A constant magnetic field H is provided in the direction shown. Anlectron is projected at uniform velocity into the field between theplates P along the dotted line ab parallel to the magnetic field. Attime t=0 the electron will be at position 1, and at time At secondslater it will be at position 2, etc. At position 1 the electron has novelocity in the direction of E but on encountering the electric field Ebetween positions 1 and 2 it will be accelerated in this direction. Ifthe angular frequency w, of the oscillating electric field E were equalto the angular ro tation frequency,

each electron would remain in phase with the electric field and would becontinuously accelerated so that it would receive more and more energyfrom the oscillating field and its motion would be a spiral of everincreasing radius. This condition would produce an electron current inphase with E at all positions, 1, 2, and would constitute a loading orresistive component of current. If the condenser plates P were to formpart of a resonant circuit, 'by connecting an inductance between theplates, this in phase component would have no effect On the frequency,but would reduce the Q of the circuit.

The transit time of the electron through the condenser plates and therelative values of to and w can be chosen so that the net electroncurrent is not in the direction of E but is in quadrature to B so thatit constitutes a purely reactive current. To see how this comes about,let w be somewhat less than (0 In this circumstance the electron willnot complete one revolution during one complete cycle of the oscillatingfield. Consequently, it will lag behind E by a certain phase angle Ao,so that as the time goes on the electron lags more and more behind E. Itwill, however, continue to be accelerated until it lags electron iszero.

behind E by 90 degrees. The electron then still increases its laggingphase angle by Aqb on each revolution but the electron now is retardedby the oscillating field and loses energy. It is evident that for agiven value of -10 the time of flight of the electron between thecondenser plates, can be adjusted so that the energy acquired from thefield in the period during which acceleration took place is just givenback to the field during the period of retardation and the net energytransfer from field to This situation is illustrated in Figs. 2, 3, and4. When an electron enters the plates P at position 1, Fig. 4, it has nodisplacement from the median plane between the plates. This zerodisplacement is shown in Fig. 3. Also the transverse current at position1 is zero as is shown in Fig. 2. At position 2, Fig. 4, the

electron has acquired some circular motion and its displacement from themedian plane is shown by the vector .r. in Fig. 3. Since w w theelectron lags behind E by the phase angle t: when it reaches position 2.The trans- 'verse electron current in magnitude and phase relative to Eis shown by the vector i in Fig. 2. When the electron has reachedposition 3, its displacement is given by r, and the transverse currentby i It is evident that at position 3 the magnitude of the current i isgreater than at position 2 as also is the lagging phase angle. Atposition 5, the electron has acquired its maximum displacement and thecurrent i due to it is 90 out of phase with E and is purely reactive.From this point on the electron is retarded and the current produced byit has a negative resistive component that is a component opposite to E.When electrons enter the condenser plates at all times as in acontinuous beam, there will be electrons at all positions from 1 to 9simultaneously and the total effective current will be the vector sum ofthe currents at each position. This vector sum is shown by I in Fig. 2.Thus the total effective current lags behind the field E by 90. Thus Eand l are related in phase exactly the same as the potential difierenceacross an inductance and the current through it. If the condenser platesshown were in parallel with an inductance to form a resonant circuitwith resonant frequency w the passage of the beam of electrons throughthe condenser plates would increase the resonant frequency.

On the other hand, if w td then the currents i i etc. would lead E and(d -L0 would be so chosen that the total current would lead E by 90giving rise to a decrease in the resonant frequency of the parallelcircuit.

In efiect, what the above means is that when the electrons lag thealternating electric field there is in effect an r inductive reactanceplaced in parallel with the inductive reactance connected across theplates and the equivalent circuit is shown in Fig. 5. Inasmuch as thiscauses a reduction in the inductance reactance of the given frequency,the inductive and capacitive reactances do not provide resonance at thisfrequency. The frequency of the driving voltage must be raised to bringabout resonance again. This causes the capacitive reactance to decreaseand the inductive reactance to increase so that resonance is establishedat the higher frequency. Likewise, when the electrons are ahead of theelectric field, the resultant eifect is to place a capacitance inparallel with the capacitance of the plates, the equivalent circuitbeing shown in Fig. 6. This reduces the capacitive reactance of theresonator and in order to establish resonant conditions, the frequencymust be lowered so that the inductive reactance decreases and thecapacitive reactance increases. Thus, there is provided the means forvarying the resonant frequency of the system above and below that whichthe system would have with no electron beam present. This is the actionwhich takes place in a cavity resonator which is the equivalent of theresonant circuit discussed.

The eifect of changing the transit time of the electrons through theplates can be seen from the following. Short- 6 ening the transit timefor a given w -w would have the same eifect as that produced byshortening the plates. Thus, if the plates Were terminated at position 7in Fig. 4, the elfective current between the plates would be given bythe dotted vector in Fig. 2. In this case the inductive component ofcurrent has been decreased and a resistive component of current ispresent. Hence changes in the transit time can also be used to changethe frequency of a resonant system composed of'the condenser plates anda parallel inductance. On the other hand, varying the current densityvaries the length of the resultant vector i along the X axis since eachof the components i and i is varied. Thus the inductive reactance is ineifect varied and hence the frequency.

Thefrequency shift produced by projecting an electron beam along amagnetic field H and through an oscillating electric field E offrequency w between two parallel plates of length L and distance a aparthas been shown, on pages 644-647 of the above-mentioned paper, to beapproximately 2 in ni se V 00 0 where [In] is the total beam current, V0is the beam voltage, Co is the total equivalent capacitance of thesystem,

0=(w w )-r and 'r is the electron transit time (see Equation 14, page647 of said paper). For a given value of 1, Aw(0) is a maximum when 0=(ww )T=i1r radians:

L 11 i 1 I Ami) 8d 11 10,,

Since 0 may be expressed or (/c1)a, where It is the ratio w /w and a isthe transit angle of the electron in radians.

The same means for changing frequency can be incorporated in a highfrequency generator to obtain a generator which can be internallyfrequency modulated. It is especially advantageous to apply the meanseX- plained above to frequency modulate a magnetron be causearrangements can be made to use the same magnetic field used for themagnetron. Such a magnetron incorporating my invention and utilizing amulti-resonator system is shown in Figs. 8 to 12, inclusive.

In this arrangement an anode block 30 is provided with a central opening31 extending therethrough. A plurality of anode segments 32 provided byradially directed vanes 32' mounted in the opening 31, as shown in Fig.10, having a central space in which is axially mounted an indirectlyheated cathode 33. It is obvious that, instead of the vane type anodearrangement, the block could be provided with radial slots for obtaininganode segments, or other forms of spaces between anode segments could beprovided. The spaces or slots provide cavity resonators 32 which in theform shown are provided between adjacent anode vanes 32' by the vanesand'the wall of the opening 31 in the anode block. If desired, the"arious anode vanes may be strapped together at one or both ends bymeans of conducting ring members 70 and 71, the rings being conductivelyconnected to alternate vanes, as shown in Figs. 9 and 10, to facilitateoperation in the desired mode.

Magnetic inserts 34 and 35 are carried by bridge members 36 and 37 whichare mounted on the anode block 30 in insulating relationship to theblock by means of bolts 38, nuts 39 insulating sleeves-40 and 40', 41and 7 41 and 42 and 42'. The cathode 33' is supported by the magneticinsert 34. One lead 43 of the cathode heater 33 is connected to theinsert 34 which is in electrical contact with the cathode 33 and bridgemember 36, and the other lead 43' extends through an eyelet and issealed through a header 45 forming part of the envelope by means of aglass bead and seal 43". The bridge member 36 is electrically connectedto a lead 44 which extends through and is sealed in the header 45 bymeans of an insulating tube 44'. The anode block 36 may be supportedfrom the header 45 by means of the supports 46 and 47. An outputcoupling loop i disposed in one of the cavity resonators terminates in acoaxial line 5152 sealed at its outer end by means of an insulating bead53. As shown in Figs. ll and 12, the anode block 30, the envelope 4555and the outer conductor of coaxial line 51-52 are in contact, and hence,are maintained at the same potential. A magnet having poles 56 and 56cooperates with the magnetic inserts 34 and 35 to provide the usualmagnetic field in the cathode space and also provide a magnetic field inthe resonators parallel to the cathode 33 and the resonator Walls.

In accordance with my invention, '1 provide one or more electron gunseach comprising an indirectly heated cathode sleeve 6% supported by theinsert 35 by means of an insulating collar 61. The leads 62 and 63 foreach cathode heater 61] extend through and are sealed by an insulatingtubular member 64 in the header 45. One lead 63 is electricallyconnected to the sleeve 60. A grid 66 is insulatingly mounted on the endof each cathode sleeve by means of an insulating collar 66 and a flangedsleeve 66" having a lead 65 sealed through an insulating tubular member65 in the header. Each electron gun is located adjacent one side of acavity resonator 32" in position to project a modulating electron beamthrough the portion of the resonator adjacent the cathode in a directionparallel to the magnetic field. An anode electrode 67 is providedadjacent the opposite side of the cavity resonator in the path of themodulating beam to serve as a collector therefor. The collector 67 isprovided with a lead 68 sealed through an insulating tubular member 68.

The operation of the magnetron of Figs. 8-12 is similar to that of Fig.l, the principal difference being that the cavity resonators 32 of themagnetron are excited by the space charge rotating in the cathode spacewhile the cavity resonator 11 of Fig. 1 is excited by an external source26 coupled thereto. The cathode sleeve 60 and grid 66 may be biasednegatively with respect to the anode block 30 by connecting the leads 63and 65 through suitable biasing sources 72 and 73 to the tube envelope,as shown in Fig. 11.

To frequency modulate the magnetron a signal may be applied to thecontrol grid 66 by an input circuit including a transformer '74. As analternative, however, the grid may be eliminated and the velocity of theelectrons controlled by applying an alternating voltage be tween theanode block 30 and cathode 60 as in Fig. 1.

For a given tapered cavity, as shown in Figs. 8-12, the optimum locationof the modulating beam radially along the resonator for maximumfrequency shift will lie as near to the point of maximum electric fieldand minimum distance between the vanes, at their inner edges, as isconsistent with substantial beam diameter, maximum beam current. Themodulating beams B have been illustrated in positions just outside thestrapping ring "iii. If desired, the strapping rings may be made smalleror larger, or even eliminated, and the beams located closer to the inneredges of the vanes.

Electrode 67 may be used as a reflector like electrode 16 of Fig. 1 inwhich case the electrons will be repelled back through the resonator andcollected by the anode vanes, thus varying the transit time of theelectrons through the resonator. As in Fig. 1, the electrode 67 may bebiased positively or negatively with respect'to the cathode at byconnecting lead 68 to a biasing voltage source 75, as shown in Fig. 12.A modulating signal voltage may be superimposed upon the bias voltage ofelectrode 67, by means of an input circuit including a transformer 76 inseries with the source 75 and the cathode lead 63.

Although two modulating beams have been shown in Figs. 8-12, it isobvious that the modulating beams could be projected through only one ormore than two resonators. The cylindrical beams shown could be replacedby an annular beam and collector. These are all equivalents of thearrangement shown.

The invention may be applied to magnetrons having any number of anodesegments and resonators.

While l 'lZlVC indicated the preferred embodiments of my invention ofwhich I am now aware and have also indicated only two specificapplications for which my invention may be employed, it will be apparentthat my invention is by no means limited to the exact forms illustratedor the use indicated, but that many variations may be made in theparticular structure used and the purpose for which it is employedwithout departing from the scope of my invention as set forth in theappended claims.

The embodiment of my invention illustrated in Fig. l is claimed in myabove-mentioned Patent No. 2,695,373.

What is claimed is:

1. An electron discharge device having an anode comprising a pluralityof spaced anode elements defining a central. space, adjacent elementsbeing connected by hollow resonators, a cathode arranged adjacent saidanode elements to supply electrons within said central space forexciting said resonators to produce a transverse alternating electricfield within said resonators, means adjacent said anode for providing 'amagnetic field within said space and resonators and extendingsubstantially normal to said electric field, and means for directing astream of electrons within a hollow resonator in a directionsubstantially parallel to the magnetic field to vary the impedance ofsaid resonator.

2. An electron discharge device having an anode comprising a pluralityof spaced anode elements defining a central space, adjacent elementsbeing connected by hollow resonators, a cathode arranged adjacent saidanode elements to supply electrons within said central space forexciting said resonators to produce a transverse alternating electricfield within said resonators, means adjacent said anode for providing amagnetic field within said space and resonators extending substantiallynormal to said electric field, means for directing a stream of electronswithin a hollow resonator in a direction substantially parallel to themagnetic field, and control means for varying the flow of the electronsin said stream, whereby the impedance of said resonator is varied.

3. An electron discharge device having an anode comprising a pluralityof spaced parallel anode elements de fining a central. space, adjacentelements conected by hollow resonators, a cathode arranged adjacent saidanode elements to supply electrons within said central space forexciting said resonators to produce a transverse alternating electricfield therein, means adjacent said anode for providing a magnetic fieldwithin said space and resonators extending substantially parallel tosaid elements and normal to said electric field, means adjacent saidanode for directing a stream of electrons through a hollow resonator ina direction substantially parallel to the. magnetic field, and means forcontrolling the How oi said stream comprising a reflector electrodeoppositely disposed to the last named means.

4. An electron discharge device having an anode comprising a pluralityof spaced anode elements defining a central space and lying parallel toa central axis, cavity resonators connected between adjacent elements,an

elongated cathode within said central space and lying along the centralaxis of said anode elements for supplying electrons within said spacefor exciting said resonators to produce an alternating electric fieldtherem, means adjacent said anode for providing a magnetic field withinsaid space and resonators extending substantially parallel to saidcathode and elements, means for directing a stream of electrons within aresonator in a direction substantially parallel to said magnetic field,and a control grid in the path of said stream for varying said stream ofelectrons during operation of said device for varying the impedance ofsaid resonator.

5. An electron discharge device having an anode comprising a pluralityof spaced anode elements defining a central space and lying parallel toa central axis, cavity resonators connected between adjacent elements,an elongated cathode Within said central space for supplying electronswithin said space and lying along said axis, means adjacent said anodefor providing a magnetic field within said central space and resonatorsextending parallel to said cathode and elements, means for directing astream of electrons within a resonator in a direction substantiallyparallel to the magnetic field, a control grid in the path of saidstream of electrons for varying said stream during operation of saiddevice, whereby the impedance of said resonator may be varied, and acollector electrode oppositely disposed to the last named means.

6. An electron discharge device having an anode comprising a pluralityof spaced anode elements defining a central space and lying parallel toa central axis, cavity resonators having a resonant frequency andconnected between adjacent elements and each enclosing a space, acathode arranged adjacent said anode elements to supply electrons withinsaid central space for exciting said resonators to produce :a transversealternating electric field of said resonant frequency Within saidresonators, means adjacent said anode for providing a magnetic fieldwithin said central space and the spaces enclosed by said resonators andextending normal to the alternating electric field within saidresonators, and means for varying the frequency of oscillation of saidresonators comprising means for directing a stream of electrons within aspace confined by one of said resonators in a direction substationallyparallel to said magnetic field and normal to said electric field, anelectrode'oppositely disposed to the last named means, and other meansfor controlling said stream of electrons.

7. An electron discharge device having an electrode assembly includingan anode block having :a plurality of spaced anode segments extendingradially toward and defining a central space, the spaces betweenadjacent segments providing hollow cavity resonators of predeterminedresonant frequency, :an elongated cathode for supplying electrons withinsaid central space for exciting said resonators to produce transversealternating electric fields at said frequency within said resonators,means supporting said cathode in said central space in insulatingrelationship with respect to said anode block, means adjacent saidelectrode assembly for providing a magnetic field within said centralspace and said resonators normal to said electric fields, and means forvarying the resonant frequency of said resonators comprising means fordirecting a stream of electrons within a resonator in a directionsubstantially parallel to the magnetic field.

8. An electron discharge device having an electrode assembly includingan anode block having a plurality of spaced anode segments extendingradially toward and defining a central space, the spaces betweenadjacent anode segments providing hollow cavity resonators, a cathodeadjacent said anode segments for supplying electrons within said centralspace for exciting said resonators to produce alternating electricfields within said resonators and means insulatingly supporting saidcathode with respect to said anode block and including a bridging memberextending across said resonators and said central space, means adjacentsaid electrode assembly for providing a magnetic field within saidcentral space and said resonators 10 normal to said electric fields, anda second cathode adja cent said anode block for directing a stream ofelectrons into a resonator in a direction substantially parallel to saidmagnetic field.

9. An electron discharge device having an electrode assembly includingan anode block having a plurality of spaced anode segments extendingradially toward and defining a central space, the spaces betweenadjacent anode segments providing hollow cavity resonators, a cathodeadjacent said anode segments for supplying electrons within said centralspace for exciting said resonators to provide alternating electricfields within said resonators, means adjacent said electrode assemblyfor providing a magnetic field within said central space and within saidresonators normal to said electric fields, said means including magneticinserts on opposite sides of said anode block, said cathode beingsupported by one of said in-- serts, a second cathode adjacent saidanode block for directing a stream of electrons into a resonator in adirection substantially parallel to said magnetic field, said secondcathode being supported by one of said inserts, and means forcontrolling the stream of electrons from said second cathode, wherebythe frequency of operation of said electron discharge device may bevaried.

10. An electron discharge device having an anode comprising a series ofhollow resonators opening into a cathode space, means adjacent saidanode for establishing a constant magnetic field within said space andresonators, a cathode arranged adjacent said anode to supply electronswithin said space for exciting said resonators to produce a transversealternating electric field Within said resonators, and means fordirecting a stream of electrons through one of said resonators.

ll. An electron discharge device having an anode'comprising a pluralityof spaced parallel anode elements defining a central space, adjacentelements being connected by hollow resonators, means adjacent said anodefor providing a magnetic field within said space and resonators parallelto said anode elements, cathode means adjacent said anode elements forsupplying electrons within said central space, said anode and cathodemeans being adapted to be manitained at positive and negative directcurrent potentials, respectively, for exciting said resonators toproduce transverse alternating electric fields therein, and means fordirecting a stream of electrons within a resonator in a direction havinga substantial component parallel to said magnetic field and normal tosaid electric fields.

12. A magnetron having an anode comprising a plurality of spacedparallel anode segments surrounding a central space, adjacent segmentsbeing connected by hol-- low resonators, said segments and resonatorshaving capacitance and inductance determining their normali resonantfrequency, means adjacent said anode for pro-- ducing a magnetic fieldwithin said central space and the portions of said resonators adjacentsaid central space in a direction substantially parallel to said anodesegments, a cathode arranged adjacent said anode elements to supplyelectrons within said central space for exciting said resonator toproduce a transverse alternating electric field within said resonators,and means for varying the resonant frequency of said resonatorscomprising means for direct ing a stream of electrons within one of saidresonator portions adjacent said central space in a directionsubstantially parallel to the magnetic field.

13. A magnetron comprising at least one hollow resonator havinginductance and capacitance and a normal mode of oscillation at aresonant angular frequency determined by said inductance andcapacitance, means including a cathode adjacent said resonator forestablishing an oscillating electric field of said frequency and modebetween two opposite walls of said resonator, means adjacent saidresonator for providing a constant magnetic field within said resonatorin a direction substantially parallel to said opposite walls, and meansfor directing a stream of electrons between said opposite walls in a.

1 1 direction substantially parallel to said magnetic field, the fieldstrength of said" magnetic field being slightly different from where wis said resonant angular frequency, and m and e are the mass andelectrical charge of an electron, respectively, whereby the electronstraversing the crossed electric and magnetic fields within saidresonator will execute spiral paths slightly out of phase with theoscillating electric field, producing a reactive efiect which changesthe resonant angular frequency of the magnetron.

14. A magnetron according to claim 13, including control means forvarying the flow of said electrons in said stream.

15. A- magnetron according. to claim 14, wherein said control meanscomprises a grid electrode disposed in the path ofsaid-stream ofelectrons.

1.6. A magnetron according to claim 13, including a reflector electrodeoppositely disposed to said means for directing a stream of electronsbetween said opposite walls. W

17. A magnetron having a cathode, an anode structure adjacent saidcathode and comprising a series of cavity resonators open toward saidcathode, and means for varying the impedance of said resonators.comprising means forv directing a stream of electrons through at leastone of said resonators in the region near the cathode where a strongoscillating electric field is generated during the operationrof themagnetron;

18. A magnetron comprising at least one hollow resonator havinginductance and capacitance and a normal mode of oscillation at aresonant angular frequency determined by said inductance andcapacitance, means including a cathode adjacent said resonatorfor'cstablishing an oscillating electric field of said frequency andmode between two opposite walls of said resonator, means adjacentsaidresonator for providing a constant magneticfield within saidresonator in a direction substantially parallel to said opposite Walls,and means adjacent said resonator for directinga beam of electronsthrough said resonator between said opposite. walls in a directionsubstantially parallel to said magnetic field, the intensity H of saidmagnetic field and the transit time T of the electrons through saidresonator being so related to said resonant angular frequency wthat(H/mw )'r is substantially equal to 7r radians, where e and m are thecharge and. mass, respectively, of an electron andar is 3.1416, wherebyduring operation of said magnetron the electrons of saidbeam executespiral paths through said resonator out of phase with said oscillatingfield and thus produce a maximumreactive effect for a given beam currentupon said resonator to change the resonant angular frequency of. themagnetron.

19. An electron-discharge devicecomprising: a cathode; an anodestructure, spaced from said cathode, and

including a cavity resonator; means, supported adjacent said cathode andsaid anode structure, for establishing. a magnetic field through saidcavity resonator in a direction transverse to the electron-path betweensaid cathode and said anode structure; a source of; electrons supportedadjacent. said cavity resonator; and means, intermediate said source ofelectrons and said cavity resonator, for directing the electrons emittedby said source into said cavity resonator along "a path within andsubstantially parallel to said magnetic field, whereby sai'ddevice maybe tuned to a frequency other than its natural resonant frequency.

20. An electrode-discharge device comprising: a cathode; an anodestructure, spacedtfrom said cathode, and: including a plurality of anodemembers; each pair of adjacent, anode members togetherrwiththat portioniof said anode structure. lying tlierebetween,defining. a cavity 12resonator; means supported adjacent said cathode and said anodestructure, for establishing a magnetic field through said cavityresonators; a source of electrons supported adjacent said cavityresonators, and means", inter-- mediate said source of electrons andsaid cavity resonators for directing the electrons emitted by saidsource into said cavity resonators along a path within and substantiallyparallel to said magnetic field, whereby said device may be tuned to afrequency other than its natural resonant frequency.

21; An electron-discharge device comprising: a cathode; an anodestructure, spaced from said cathode, and including a. cavity resonator;means, supported adjacent said cathode and said anode structure, forestablishing a magnetic field in a direction transversely of theelectronpath between said cathode and said anode structure; saidmagnetic field having a po1tion thereof extending through said cavityresonator; a source of electrons, supported adjacent said cavityresonator, and adapted to have a voltage established between itself andsaid anode structure for directing the electrons emitted thereby intosaid cavity resonator along a path within and substantially parallel tosaid magnetic field, whereby said device may be tuned to a frequencyother than its natural resonant frequency; and means, supportedintermediate said source of electrons and said anode structure, forcontrolling the density of the electron-flow between said source andsaid anode structure.

22. An eIectrOn diScharge device comprising: a cath ode; art-anodestructure, spaced from said cathode, and

including a plurality of anode members; each pair of adjacent anodemembers, together with that portion of said anode structure lyingthercbetween, defining a cavity resonatcrymeans, supported adjacent saidcathode and 1 said anode structure, for establishing a magnetic field ina direction transversely of the electron-path between said cathode andsaid anode structure; said magnetic field having a portion thereofextending through said cavity resonators; a source ofelectrons,supported adjacent said cavity resonators, and adapted to have a voltageestab lished between itself and said anode structure for directing theelectrons emitted thereby into said cavity resonators along a pathwithin and substantially parallel to said magnetic field, whereby saiddevice may be tuned to a frequency other than its natural resonantfrequency; and means, supported intermediate said source of electronsand said. anode structure, for controlling the density of theelectron-flow between said source and said anode structure.

23. A magnetron having a cathode, an anode structure adjacent saidcathode and comprising a series of cavity resonators open toward saidcathode, and means for varying the impedance of said resonatorscomprising cathode means separate from said cathode for supplyingelectrons within one of said resonators.

24. A magnetron according to claim 23, further including means forvarying the flow of said electrons.

25. A magnetron according to claim 23, further including a control gridadjacent'said cathode means.

26'. A magnetron according to claim 23, further including a reflectorelectrode oppositely disposed to said cathode means.

27. A magnetron according to claim 23. further including means connectedbetween said cathode means and said anode structure for applying avariable voltage therebetween.

28. An electron discharge device comprising a cathode, an anodest'ructure'spaced from said cathode and including a pair of anode facesinterconnected by a cavity resonator open'at'both ends, means adjacentsaid cathode for maintaining a magnetic held through said cavityresonator in a' direction extending between said open' of-sai'd openends, and an electron reflecting electrode facing the othe'r ofsai'dopen ends.'

29. An electron discharge device comprising a cathode, an anodestructure spaced from said cathode and including a pair of anode face;interconnected by a cavity resonator open at both ends, means adjacentsaid cathode for maintaining a magnetic field through said cavityresonator in a direction extending between said open ends, and a pair ofelectrodes, at least one of which is a thermionic electron-emittingelectrode, facing said open ends.

30. A frequency modulating oscillator system including an electrondischarge device comprising a cathode, an anode structure spaced fromsaid cathode and including a pair of anode faces interconnected by acavity resonator open at both ends, means adjacent said cathode formaintaining a magnetic field through said cavity in a directionextending between said open ends, a pair of electrodes, at least one ofwhich is a thermionic electronemitting electrode, facing said open ends,means, connected intermediate said electrodes and said anode structure,for biasing each of said electrodes negatively with respect to saidanode structure, and means, connected in series with said biasing means,for superimposing a modulating signal voltage on at least one of saidelectrodes.

31. An electron discharge device comprising a cathode, an anodestructure spaced from said cathode and including a pair of anode facesinterconnected by a cavity resonator open at both ends, means adjacentsaid cathode for maintaining a magnetic field through said cavityresonator in a direction extending between said open ends, a thermionicelectron-emitting electrode facing one of said open ends and an electronreflecting electrode facing the other of said open ends, said electronemitting and reflecting electrode being electrically isolated from saidcathode.

32. An electron discharge device comprising a cathode, an anodestructure spaced from said cathode and including a pair of anode facesinterconnected by a cavity reso nator open at both ends, means adjacentsaid cathode for maintaining a magnetic field through said cavityresonator in a direction extending between said open ends, and a pair ofelectrodes, at least one of which is a thermionic electron-emittingelectrode, facing said open ends, said electrodes being electricallyisolated from said cathode.

33. A tunable electron-discharge device comprising: a cathode; an anodestructure spaced from said cathode, and incorporating a cavity resonatorin which radio-frequency oscillations are adapted to be generated; meansadjacent said cavity resonator for establishing a magnetic fieldtherethrough; means, cooperable with the electricfield component of saidradio-frequency oscillations, and with said magnetic field, for settingup a space charge in said cavity resonator; and means, coupled betweensaid cavity resonator and said last-named means, for varying the densityof said space charge.

34. An electron-discharge device comprising a cathode, an anodestructure spaced from said cathode and including .a pair of anode facesinterconnected by a cavity resonator open at both ends, means formaintaining a magnetic field through said cavity in a directionextending between said open ends, a source of electrons facing one ofsaid open ends, and an electron-reflecting electrode facing the other ofsaid open ends.

35. An electron-discharge device comprising a cathode, an anodestructure spaced from said cathode and including a pair of anode facesinterconnected by a cavity resonator open at both ends, means formaintaining a magnetic field through said cavity in a directionextending between said open ends, and a pair of electrodes facing saidopen ends, .at least one of said electrodes being electron emissiveduring operation.

36. The method of loading a high frequency generator having a cathodeand an anode cavity resonator, comprising the steps of providing aconstant magnetic field extending through said resonator, projecting anelectron beam through said resonator along said magnetic field,

adjusting the intensity of said magnetic field as a function of theoperating frequency of said generator to provide maximum loading andnegligible reactive effect by said electron beam, and varying theenergy-absorbing ability of said beam to vary the loading of saidgenerator.

37. The method of loading a high frequency magnetron generator having acentral cathode and a plurality of anode cavity resonators surroundingsaid cathode, comprising the steps of projecting an electron beamthrough one of said resonators in a direction parallel to said cathode,providing a magnetic field extending parallel to said beam and throughsaid one of said resonators, connecting said generator to a source ofoperating potentials to provide high frequency oscillations therefrom,adjusting the intensity of that portion of said magnetic field whichextends through said resonators to a value at which the electronrotation frequency thereof is substantially equal to the angularfrequency of said oscillations, and varying the conductance of said beamto vary the loading of said generator.

38. A magnetron comprising a first electron-emissive cathode and ananode disposed. adjacent said cathode, means connected with and forapplying operating potentials to said anode and cathode and therebyobtaining electron flow on paths from the cathode toward said anode togenerate microwave oscillations on said anode, a secondelect-ron-emissive oath-ode opposed to another part of said anode foralso directing electrons to the anode but to said other part thereof onpaths other than the aforesaid paths of electron flow, and for therebymodifying the said microwave oscillations, and means in the path of andfor controlling the electrons emitted from said second cathode.

39. An electron-discharge device comprising: a cathode; an anode,incorporating a cavity resonator, spaced from said cathode; means,adjacent said anode, for est-ablishing a unidirectional magnetic fieldin said cavity resonator; and means, incorporated .in said device, forprojecting a stream of electrons into said cavity resonator to controlthe resonant frequency of said device.

40. An electron-discharge device comprising: a ca-thode; an anode,incorporating a cavity resonator, spaced from said cathode; means,adjacent said anode, for establishing a unidirectional magnetic field insaid cavity resonator; means, incorporated in said device, forprojecting a stream of electrons into said cavity resonator to controlthe resonant frequency of said device; and means, coupled to saidlast-named means, for varying the density of said stream of electrons tofrequency modulate said device.

41. An electron-discharge device comprising: a cathode; an anode spacedfrom said cathode; said anode including a pair of anode arms which,together with that portion of said anode lying therebetween, define-s acavity resonator; means, adjacent said anode, for establishing amagnetic field through said cavity resonator in a direction transverseto the discharge path between said cathode and said anode; and a sourceof electrons, communicating with said cavity resonator and adapted toproject electrons therein, for altering the resonant frequency thereof.

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